1. Field of the Invention
The present invention relates to a SiC (Silicon Carbide) semiconductor device including a trench-gate type vertical power device, and a method of manufacturing the same.
2. Description of Related Art
In recent years, SiC has gathered attention because of its use as material in the production of power devices due to its high electric field breakdown strength. SiC having a higher electric field breakdown strength than silicon, makes it possible to control a large current in a power device. For example, SiC semiconductor devices are expected to be used in motor control for a hybrid vehicle.
To pass a further larger current in a power device, it is effective to increase the channel density of the power device. Accordingly, in the field of silicon transistors, trench-gate type vertical power MOSFETs are now in actual use. The trench-gate structure is applicable to SiC transistors. However, in the case of SiC, there is a challenge in using the trench-gate structure as set forth below.
Generally, a SiC transistor in operation is applied with a voltage which is nearly 10 times that applied to a silicon transistor in operation, because SiC has electric field breakdown strength about 10 times higher than that of silicon. Accordingly, the strength of the electric field applied to the gate insulation film on the trench surface in the case of the SiC transistor is also nearly 10 times higher than that in the case of the silicon transistor.
To cope with this, it has been proposed to form, immediately after the trench is formed, a p-type layer at the bottom portion of the trench gate by ion-injection of p-type dopant in manufacturing a trench-gate type MOSFET. For more detail, refer to Japanese Patent Application Laid-open No. 10-98188.
However, the structure disclosed in this patent document cannot prevent destruction of the gate insulation film, because the p-type layer is formed only in the bottom portion of the trench gate, and accordingly, the electric field concentrates on the sides of the bottom portion of the trench gate.